erl_call - Call/start a distributed Erlang node.
Please see following description for synopsis
erl_call(1) User Commands erl_call(1)
NAME
erl_call - Call/start a distributed Erlang node.
DESCRIPTION
erl_call makes it possible to start and/or communicate with a distrib-
uted Erlang node. It is built upon the Erl_Interface library as an
example application. Its purpose is to use a Unix shell script to
interact with a distributed Erlang node. It performs all communication
with the Erlang rex server, using the standard Erlang RPC facility. It
does not require any special software to be run at the Erlang target
node.
The main use is to either start a distributed Erlang node or to make an
ordinary function call. However, it is also possible to pipe an Erlang
module to erl_call and have it compiled, or to pipe a sequence of
Erlang expressions to be evaluated (similar to the Erlang shell).
Options, which cause stdin to be read, can be used with advantage, as
scripts from within (Unix) shell scripts. Another nice use of erl_call
could be from (HTTP) CGI-bin scripts.
EXPORTS
erl_call <options>
Starts/calls Erlang.
Each option flag is described below with its name, type, and
meaning.
-a [Mod [Fun [Args]]]]:
(Optional.) Applies the specified function and returns the
result. Mod must be specified. However, start and [] are
assumed for unspecified Fun and Args, respectively. Args is
to be in the same format as for erlang:apply/3 in ERTS
except only a subset of all terms are allowed. The allowed
term types are: list (and string representation of list,
that is "example"), tuple, atom and number.
Notice that this flag takes exactly one argument, so quoting
can be necessary to group Mod, Fun, and Args in a manner
dependent on the behavior of your command shell.
-address [Hostname:]Port:
(One of -n, -name, -sname or -address is required.) Hostname
is the hostname of the machine that is running the peer node
that erl_call shall communicate with. The default hostname
is the hostname of the local machine. Port is the port num-
ber of the node that erl_call shall communicate with. The
-address flag cannot be combined with any of the flags -n,
-name, -sname or -s.
The -address flag is typically useful when one wants to call
a node that is running on machine without an accessible epmd
instance.
-c Cookie:
(Optional.) Use this option to specify a certain cookie. If
no cookie is specified, the ~/.erlang.cookie file is read
and its content is used as cookie. The Erlang node we want
to communicate with must have the same cookie.
-d:
(Optional.) Debug mode. This causes all I/O to be output to
the ~/.erl_call.out.Nodename file, where Nodename is the
node name of the Erlang node in question.
-e:
(Optional.) Reads a sequence of Erlang expressions, sepa-
rated by comma (,) and ended with a full stop (.), from
stdin until EOF (Control-D). Evaluates the expressions and
returns the result from the last expression. Returns
{ok,Result} on success.
-fetch_stdout:
(Optional.) Executes the code, specified with the -a or -e
option, in a new process that has a group leader that for-
wards all stdout (standard output) data so that it is
printed to stdout of the erl_call process. This means that
stdout data that are written during the execution of the
called code, by the code and by descendant processes, will
be forwarded (given that the group leader has not been
changed by a call to erlang:group_leader/2).
The printed data is UTF-8 encoded.
This option is only relevant together with the option -a or
-e.
See the documentation of the I/O protocol, for more informa-
tion about the group leader concept.
Note:
This option only works when erl_call is interacting with a
node with a version greater or equal to OTP-24.
-h HiddenName:
(Optional.) Specifies the name of the hidden node that
erl_call represents.
-m:
(Optional.) Reads an Erlang module from stdin and compiles
it.
-n Node:
(One of -n, -name, -sname or -address is required.) Has the
same meaning as -name and can still be used for backward
compatibility reasons.
-name Node:
(One of -n, -name, -sname or -address is required.) Node is
the name of the peer node to be started or communicated
with. It is assumed that Node is started with erl -name,
which means that fully qualified long node names are used.
If option -s is specified, an Erlang node will (if neces-
sary) be started with erl -name.
-no_result_term:
(Optional.) Do not print the result term. This option is
only relevant together with the options -a and -e.
-q:
(Optional.) Halts the Erlang node specified with switch -n.
This switch overrides switch -s.
-r:
(Optional.) Generates a random name of the hidden node that
erl_call represents.
-R:
(Optional.) Request a dynamic random name, of the hidden
node that erl_call represents, from the peer node. Supported
since OTP 23. Prefer -R over -r when doing repeated requests
toward the same peer node.
-s:
(Optional.) Starts a distributed Erlang node if necessary.
This means that in a sequence of calls, where '-s' and '-n
Node' are constant, only the first call starts the Erlang
node. This makes the rest of the communication very fast.
This flag is currently only available on Unix-like platforms
(Linux, Mac OS X, Solaris, and so on).
-sname Node:
(One of -n, -name, -sname or -address is required.) Node is
the name of the peer node to be started or communicated
with. It is assumed that Node is started with erl -sname,
which means that short node names are used. If option -s is
specified, an Erlang node is started (if necessary) with erl
-sname.
-timeout Seconds:
(Optional.) Aborts the erl_call process after the timeout
expires. Note that this does not abort commands that have
already been started with -a, -e, or similar.
-v:
(Optional.) Prints a lot of verbose information. This is
only useful for the developer and maintainer of erl_call.
-x ErlScript:
(Optional.) Specifies another name of the Erlang startup
script to be used. If not specified, the standard erl
startup script is used.
EXAMPLES
To start an Erlang node and call erlang:time/0:
erl_call -s -a 'erlang time' -n madonna
{18,27,34}
To terminate an Erlang node by calling erlang:halt/0:
erl_call -s -a 'erlang halt' -n madonna
To apply with many arguments:
erl_call -s -a 'lists seq [1,10]' -n madonna
To evaluate some expressions (the input ends with EOF (Control-D)):
erl_call -s -e -n madonna
statistics(runtime),
X=1,
Y=2,
{_,T}=statistics(runtime),
{X+Y,T}.
^D
{ok,{3,0}}
To compile a module and run it (again, the input ends with EOF (Con-
trol-D)):
(In the example, the output has been formatted afterwards.)
erl_call -s -m -a procnames -n madonna
-module(procnames).
-compile(export_all).
start() ->
P = processes(),
F = fun(X) -> {X,process_info(X,registered_name)} end,
lists:map(F,[],P).
^D
[{<madonna@chivas.du.etx.ericsson.se,0,0>,
{registered_name,init}},
{<madonna@chivas.du.etx.ericsson.se,2,0>,
{registered_name,erl_prim_loader}},
{<madonna@chivas.du.etx.ericsson.se,4,0>,
{registered_name,error_logger}},
{<madonna@chivas.du.etx.ericsson.se,5,0>,
{registered_name,application_controller}},
{<madonna@chivas.du.etx.ericsson.se,6,0>,
{registered_name,kernel}},
{<madonna@chivas.du.etx.ericsson.se,7,0>,
[]},
{<madonna@chivas.du.etx.ericsson.se,8,0>,
{registered_name,kernel_sup}},
{<madonna@chivas.du.etx.ericsson.se,9,0>,
{registered_name,net_sup}},
{<madonna@chivas.du.etx.ericsson.se,10,0>,
{registered_name,net_kernel}},
{<madonna@chivas.du.etx.ericsson.se,11,0>,
[]},
{<madonna@chivas.du.etx.ericsson.se,12,0>,
{registered_name,global_name_server}},
{<madonna@chivas.du.etx.ericsson.se,13,0>,
{registered_name,auth}},
{<madonna@chivas.du.etx.ericsson.se,14,0>,
{registered_name,rex}},
{<madonna@chivas.du.etx.ericsson.se,15,0>,
[]},
{<madonna@chivas.du.etx.ericsson.se,16,0>,
{registered_name,file_server}},
{<madonna@chivas.du.etx.ericsson.se,17,0>,
{registered_name,code_server}},
{<madonna@chivas.du.etx.ericsson.se,20,0>,
{registered_name,user}},
{<madonna@chivas.du.etx.ericsson.se,38,0>,
[]}]
To forward standard output without printing the result term (again, the
input ends with EOF (Control-D)):
erl_call -s -e -sname madonna -fetch_stdout -no_result_term
io:format("Number of schedulers: ~p~n", [erlang:system_info(schedulers)]),
io:format("Number of logical cores: ~p~n", [erlang:system_info(logical_processors_available)]).
^D
Number of schedulers: 8
Number of logical cores: 8
Ericsson AB erl_interface 5.1 erl_call(1)